The invention relates to central locking systems, especially for motor vehicles, and more particularly to a central locking system comprising a plurality of electric locking drives, a time control circuit means triggerable by at least one control switch in switching over from a first switch position into a second switch position, said circuit means switching on the locking drives for a specific time duration in a predetermined drive direction.
Central locking systems of this kind are known, for example from German publication specification No. 27 57 246. The locking drives are controlled by a timed current pulse, which is triggered by means of a control switch and so timed that the locking drives are switched on for a time period adequate either for locking or for unlocking. It has appeared that the duration of the drive pulse of known central locking systems cannot be kept sufficiently constant under the operating conditions in a motor vehicle. In the motor vehicle the time control circuit can be subjected to temperature fluctuations, for example between -40.degree. C. and +80.degree. C., while in addition the supply voltage can fluctuate between 9 and 15 volts. The influence of these operational conditions can lead to short and inadequate drive pulses, by which the locks are not locked or not unlocked, or excessively long drive pulses can result which can lead to damage to the locking drives or the locks.
The invention is directed towards improving the above-explained central locking system in a constructionally simple manner so that the drive pulses fed to the locking drives can be kept sufficiently constant even under greatly fluctuating operational conditions, especially as regards the ambient temperature and the supply voltage.